Inverter Compressor Preheating with Low Carrier Frequency
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Solution Overview
Problem
Existing methods for preheating inverter-driven compressors, such as direct-current preheating and phase interruption electrification, result in increased leakage current when the motor is immersed in lubricating oil, potentially triggering earth leakage breakers.
Innovation Solution
Operating the inverter at a carrier frequency lower than normal operation frequencies when the compressor is unpowered to energize the motor, reducing leakage current and preventing compressor breakage by gasifying refrigerant dissolved in oil.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If the inverter operates at normal carrier frequency to energize the motor during preheating, then the preheating effectiveness is improved, but the leakage current increases significantly causing earth leakage breaker malfunction
Solution Approach 1:
The patent applies parameter changes by modifying the carrier frequency parameter of the inverter from its normal operation value to a lower value during preheating mode. This parameter change reduces the leakage current that flows when the motor is energized while the compressor is stationary and immersed in lubricating oil, thereby preventing earth leakage breaker malfunction while still achieving effective preheating.
Solution Approach 2:
The patent implements dynamics by making the carrier frequency adjustable and adaptive based on the operational mode. The inverter dynamically switches between normal carrier frequency during operation and reduced carrier frequency during preheating, allowing the system to optimize performance and minimize harmful leakage currents under different operating conditions.
2Reliability
If the motor is energized to preheat the compressor, then the compressor temperature is raised preventing breakage, but the motor immersion in lubricating oil causes increased leakage current
Solution Approach 1:
The patent resolves this contradiction by changing the carrier frequency parameter to a lower value during preheating operations. This parameter modification maintains the ability to heat the compressor effectively while significantly reducing the leakage current generated when the motor runs while immersed in lubricating oil, thus preserving compressor safety without triggering false leakage breaker trips.
3Object-affected harmful factors
If the carrier frequency is reduced during preheating, then the leakage current is reduced preventing breaker malfunction, but the preheating efficiency may be affected
Solution Approach 1:
The patent optimizes the balance between leakage current reduction and preheating efficiency by carefully selecting an appropriate reduced carrier frequency value. The frequency is lowered sufficiently to minimize leakage current and prevent breaker malfunction, while being maintained at a level that still provides effective motor energization and heat generation for adequate preheating performance.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach effectively reduces leakage current and prevents earth leakage breaker malfunctions, ensuring safe preheating of the compressor without operational issues.
Implementation Method 1
the motor being supplied with an output electric power from an inverter
Implementation Method 2
the refrigerant dissolved in the lubricating oil can be gasified
Data Source
AI summary
To reduce a leakage current when a motor for driving a compressor is energized, with the compressor unoperated. Setting the carrier frequency of an inverter at a value lower than that used during normal operation to cause phase interruption electrification of the motor.